I often make use of a 2L Camelbak when the bulk of my tour is going to be in very hot and humid environments and or the distance between available water refills can be so great, as was the case this summer touring Nebraska ( silly me, I didn't realize it could be so hot and arid there). One thing for sure is I tend to drink more when wearing a Camelbak because it is so easy to catch a sip vs. having to grab for a bottle.